<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box1{
            width: 300px;
            height: 300px;
            background-color: #333333;
            margin: 10px auto;
        }
        .box2{
            width: 300px;
            height: 300px;
            background-color: red;
            position: absolute;
            top: 80%;
            left: 50%;
            margin-left: -150px;
            /* text-align + display */
            /* position + transform */
            /* flex 布局 */
        }
    </style>
</head>
<body>
    <div class="box1">我是box1</div>
    <div class="box2">我是box2</div>

</body>
</html>